1. Field of the Invention
The present invention relates to a steering control device for use in an automobile or the like.
2. Description of the Related Art
There are various methods for realizing a torque sensor for detecting a steering torque in a steering system of an automobile or the like. In particular, a variety of methods have been proposed for a signal processing unit that converts the detected steering torque into an electrical signal.
FIG. 11 is a block diagram showing a signal processing circuit in a typical conventional torque sensor disclosed in Japanese Patent No. 3051903, for example.
The torque sensor of this conventional technique includes, as a torque detecting unit mounted to a steering column, a torsion bar for converting the steering torque into a torsion angle, a torque detecting coil for converting the torsion angle converted by the torsion bar into an inductance value, and a temperature compensating coil for compensating for a temperature characteristic of the torque detecting coil.
Further, as a signal processing circuit connected to each coil, the torque sensor is provided with an exciting circuit for each coil, a differential amplifying circuit to compensate for the temperature characteristic of the coil, and a wave detecting circuit for detecting a steering torque signal.
Hereinafter, FIG. 11 is used to explain the signal processing circuit of the present torque sensor in more detail. In FIG. 11, reference numeral 12 is the torque detecting coil and reference numeral 13 is the temperature compensating coil for compensating the temperature characteristic of the torque detecting coil 12.
Reference numeral 14 is an oscillating circuit for oscillating an alternating voltage of a given frequency and reference numeral 15 is a reference voltage circuit for generating a reference voltage. The torque detecting coil 12 and the temperature compensating coil 13 are driven and excited at a given frequency based on the outputs of the oscillating circuit 14 and the reference voltage circuit 15.
Further, reference numeral 16 is the differential amplifying circuit for reading out the difference between the terminal voltages of the torque detecting coil 12 and of the temperature compensating coil 13 to compensate the temperature characteristic of the torque detecting coil 12, and also to amplify the difference between the terminal voltages.
Reference numeral 17 is a synchronous timing circuit for outputting a timing signal in accordance with the given frequency alternating current outputted from the oscillating circuit 14. Reference numeral 18 is the detecting circuit for eliminating frequency elements that are driven by the oscillating circuit 14 from the amplifying circuit 16 output signal, based on the timing outputted by the synchronous timing circuit 17, to obtain the steering torque signal.
FIG. 12 shows waveforms of each part in the signal processing circuit in the conventional torque sensor as described above. In FIG. 12, (a) indicates a waveform Vo of an alternating voltage signal of a predetermined frequency, which is output from the oscillating circuit 14. In FIG. 12, (b) is a timing signal VT produced when the alternating voltage signal waveform Vo goes through the synchronous timing circuit 17 and is inputted into the detecting circuit 18.
Here, in FIG. 12, (c) through (f) indicate waveforms at each part when a steering wheel not shown in the diagram is rotated to the right, for example, and torque is applied to the steering column.
A solid line in (c) shown in FIG. 12 indicates an output voltage V2 from the circuit with the torque detecting coil 12. A broken line in (c) shown in FIG. 12 indicates an output voltage V1 from a circuit with the temperature compensating coil 13. The voltage difference between the output voltages V1 and V2 is amplified by the differential amplifying circuit 16 as output voltage having an alternating current waveform V3 in (d) shown in FIG. 12.
Further, in (e) shown in FIG. 12, detection of the alternating current waveform Vo is performed by the detecting circuit 18 when the timing signal VT is positive, whereby an output voltage V4 having pulsating flow waveform is obtained from the voltage during a positive period of the alternating current waveform V3.
In (f) shown in FIG. 12, the output voltage V4 is smoothed and a voltage level VL, which is equivalent to an average value of the output voltage V4, is detected at a level that is higher than a non-steering time voltage level VN discussed below.
Similarly, in FIG. 12, (g) through (j) indicate waveforms at each part when the steering wheel, which is not shown in the diagram, is rotated to the left and torque is applied to the steering column. In (j) shown in FIG. 12, the output voltage V4 is smoothed and a voltage level VL, which is equivalent to an average value of the output voltage V4, is detected at a level that is lower than the non-steering time voltage level VN discussed below.
Next, since the torque is not applied at a time when the steering wheel is not being steered, the output voltages V1 and V2 have identical voltage waveforms, as in (k) shown in FIG. 12. As a result, the difference voltage at the differential amplifying circuit 16 is not generated, as in (l) shown in FIG. 12, and a change does not occur at the detecting circuit 18, as in (m) shown in FIG. 12. Accordingly, the voltage level becomes a voltage level VN, which is lower than the smoothed output level VH obtained when the above-mentioned right-rotation steering is performed, but is higher than the voltage level VL obtained when the left-rotation steering is performed, as in (n) shown in FIG. 12.
As described above, in the signal processing circuit in the conventional torque sensor, the temperature characteristic of the torque detecting coil 12 is compensated so that the steering torque signals having the voltage levels shown in (f), (j) and (n) shown in FIG. 12 are detected.
In the torque detecting unit in the conventional steering control device described above, even when the identical construction such that it is composed of the torque detecting coil and the temperature compensating coil is the same (unchanged), various methods may be considered for constructing the circuits that excite the coils and detect the terminal voltages in addition to the above-mentioned conventional technique. Therefore, various types of circuits have been proposed by each torque sensor manufacturer.
As a result, when the torque sensor composed of the circuits designated by the torque sensor manufacturers is incorporated into the torque detecting unit of the steering control device, the number of models necessary for performing signal processing on the output signals from the torque detecting unit increases, so that a vast number of development steps and management steps becomes necessary.
The present invention has been made to solve the above-mentioned problems, and has as an object to realize a steering control device which is capable of handling a variety of torque sensors with the same single signal processing circuit, and in which a cost increase is suppressed while taking sufficient failsafe measures.
A steering control device according to the present invention comprises: a torque sensor for detecting a signal corresponding to a steering torque in a steering system; a first microcontroller for outputting a steering torque signal equivalent to the steering torque; a second microcontroller for controlling an actuator based on the steering torque signal; actuator driving means for driving the actuator controlling the steering system; and storage means in which a steering torque neutral point compensation data is stored in advance. Also, the first microcontroller compensates a neutral point of the steering torque signal based on the neutral point compensation data stored in the storage means.
Also, a steering control device comprises: a torque sensor for detecting a signal corresponding to a steering torque in a steering system; a first microcontroller for outputting a steering torque signal equivalent to the steering torque; a second microcontroller for controlling an actuator based on the steering torque signal; actuator driving means for driving the actuator controlling the steering system; and storage means in which a steering torque gain compensation data is stored in advance. And the first microcontroller compensates an amplitude of the steering torque signal based on the gain compensation data stored in the storage means.
Therefore, the redundancy system is constructed in which, regardless of the type of the signal outputted from the torque sensor, the first microcontroller outputs the steering torque signal and the second microcontroller controls the actuator based on the steering torque signal outputted by the first microcontroller, whereby increased costs needed for calculating the steering torque signal in the redundancy system can be suppressed, and the steering control device in which sufficient failsafe measures have been taken can be realized.
Also, in the steering control device, the first microcontroller comprises a timer for generating a torque sensor drive signal that is a periodical signal for driving the torque sensor. And the first microcontroller comprises a plurality of signal processing programs for calculating the steering torque signal equivalent to the steering torque, based on the signal outputted by the torque sensor, and switches the signal processing programs in accordance with the torque sensor.
In the steering control device, the data stored into the storage means in advance is set from an outside of the steering control device by means of communications. The signal processing program for calculating the steering torque signal equivalent to the steering torque is set from the outside of the steering control device by means of communications. The steering torque signal performs a given phase compensation on a steering torque component included in the output signal from the torque sensor.
Also, in the steering control, the actuator is comprised of a motor. The first microcontroller comprises direction discriminating means for discriminating a direction of the steering torque signal and outputs a first direction-specific actuator drive permission signal indicating a current supply direction of the motor corresponding to the steering torque signal whose direction is determined by the direction distinguishing means. The second microcontroller outputs a second direction-specific actuator drive permission signal indicating a current supply direction of the motor corresponding to the steering torque signal whose direction is distinguished by the direction distinguishing means, and the actuator driving means outputs a current supply direction instruction signal for driving the motor in a direction so that the first direction-specific actuator drive permission signal and the second direction-specific actuator drive permission signal coincide with each other.
Also, in the steering control device, in a case where there is no output from the second microcontroller for a given period of time or longer, the first microcontroller judges that the second microcontroller is abnormal. And the first microcontroller reads out at least one of the first and the second direction-specific actuator drive permission signals and the current supply direction instruction signal, and based on a comparison between the direction-specific actuator drive permission signal and the current supply direction instruction signal which it reads out, determines whether or not the direction-specific actuator drive permission signal that it read out is abnormal. In a case where a given output signal outputted from the torque sensor continues to be outside a given range for a given period of time or longer, the first microcontroller judges that the torque sensor is abnormal. In a case where the first microcontroller judges that the torque sensor is abnormal, the first microcontroller outputs a torque neutral signal as the steering torque signal.
Also, in the steering control device, in a case where the first microcontroller judges that the torque sensor is abnormal, the first microcontroller outputs a signal outside a given range as the steering torque signal. In a case where there is no output from the first microcontroller for a given period of time or longer, the second microcontroller judges that the first microcontroller is abnormal.
Also, in the steering control device, the second microcontroller reads out at least one of the first and the second direction-specific actuator drive permission signals and the current supply direction instruction signal, and based on a comparison between the direction-specific actuator drive permission signal and the current supply direction instruction signal which are read out, determines whether or not the read direction-specific actuator drive permission signal is abnormal. In a case where a given output signal outputted from the torque sensor continues to be outside a given range for a given period of time or longer, the second microcontroller judges that the torque sensor is abnormal.
Also, a steering control device further comprises abnormality detecting means for detecting the abnormality judged by one of the first and the second microcontrollers, and the abnormality detecting means stops the operation of the actuator driving means. In the steering control device, the first and the second microcontrollers are mounted inside the same casing.